I'm concerned help please

So for the last 6 months or so I've been having an irregular period. I've always had a great period, on time every month, no cramping, and the longest it lasted was probably 7 days. So this month I've been on my period for about 22 days, literally, with about a week and a half of heavy bleeding and huge blood clots. The size of golf balls at times. I went to the ER because I couldn't walk my lower back was in so much pain and they said it's just a UTI. I took the antibiotics but the back pain is still there. I have an appointment with my primary Dr so I'm waiting on that. Has this happened to any of you? What should I do?